Dissemination of node metrics in server clusters

ABSTRACT

In some embodiments, a server node may transmit metrics to a client piggy-backed on (appended to) responses to regular read/write requests. Other embodiments may be disclosed and/or claimed.

RELATED CASES

This application is a continuation of, and claims priority to, U.S. patent application Ser. No. 15/944,638, filed Apr. 3, 2018, which is a continuation in part of Ser. No. 15/610,964, filed Jun. 1, 2017; this application is also a continuation of, and claims priority to, U.S. patent application Ser. No. 15/610,964, filed 1 Jun. 2017, both of which are incorporated herein by reference in their entireties.

COPYRIGHT NOTICE

Copyright 2018 salesforce.com, inc. A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the United States Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.

TECHNICAL FIELD

The technology relates to techniques for disseminating load data for nodes of a distributed computing system.

BACKGROUND

The background description provided herein is for the purpose of generally presenting the context of the disclosure. Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.

Distributed systems are becoming very large and are being served by tens thousands of individual machines. It is extremely unpractical to have homogeneous machines making up this clustered distributed system. In the world of heterogeneous nodes, one node's capabilities can widely vary with that of others in the same cluster either static hardware configurations or dynamic load on the system. Hardware configurations can vary on storage capacity, Storage efficiency, performance, network bandwidth, network performance, number of CPU cores, CPU capabilities, clock rate, amount of memory that are constant for a given machine. Most common implementations tend to distribute work and data across the cluster nodes in a randomized fashion. Treating all nodes equally and uniform distribution can lead to some nodes getting overwhelmed because they have limited disk capacity or have limited CPU/Memory resource or currently it is serving high workload.

BRIEF DESCRIPTION OF THE DRAWINGS

The included drawings are for illustrative purposes and serve to provide examples of possible structures and operations for the disclosed inventive systems, apparatus, methods and computer-readable storage media. These drawings in no way limit any changes in form and detail that may be made by one skilled in the art without departing from the spirit and scope of the disclosed implementations.

FIG. 1A shows a block diagram of an example environment in which an on-demand database service can be used according to some implementations.

FIG. 1B shows a block diagram of example implementations of elements of FIG. 1A and example interconnections among these elements according to some implementations.

FIG. 2 shows a simplified block diagram of a cluster of servers in a distributed data storage system.

FIG. 3A illustrates some examples of static server node metrics that may be used in realizing some embodiments consistent with the present disclosure.

FIG. 3B illustrates some examples of dynamic server node metrics that may be used in realizing some embodiments consistent with the present disclosure.

FIG. 4A is a simplified conceptual diagram illustrating a client entity retrieving node metrics from each of the server nodes in a cluster.

FIG. 4B is a simplified conceptual diagram illustrating a table storing server node metrics collected by a client in a distributed data storage system.

FIG. 5A is a simplified flow diagram of an example client process for resource aware load distribution in a distributed system.

FIG. 5B is a simplified flow diagram of an example server node process to piggyback local metrics in a response to a request.

FIG. 5C is a simplified flow diagram of an example process for a client to allocate a request to a server node in a distributed data storage system.

FIG. 6A is a simplified conceptual diagram illustrating request and reply messaging between a client and a server node.

FIG. 6B is a simplified conceptual diagram illustrating a read reply packet with appended (piggyback) server node metrics.

FIG. 7 is a simplified flow diagram of an example client process for maintaining current server node metrics to improve resource aware load distribution in a distributed system.

FIG. 8 is a simplified conceptual diagram illustrating request and reply messaging between a client and server nodes for dissemination of metrics to each server node, according to some embodiments.

FIG. 9 is a flowchart of a method for carrying out a gossip-type dissemination of server metrics, according to various embodiments.

FIG. 10 is a flowchart of a method for comparing server metric information received from a node in a cluster with server metric information stored in a client to determine an update to disseminated server metrics, according to various embodiments.

DETAILED DESCRIPTION

Examples of systems, apparatus, computer-readable storage media, and methods according to the disclosed implementations are described in this section. These examples are being provided solely to add context and aid in the understanding of the disclosed implementations. It will thus be apparent to one skilled in the art that the disclosed implementations may be practiced without some or all of the specific details provided. In other instances, certain process or method operations, also referred to herein as “blocks,” have not been described in detail in order to avoid unnecessarily obscuring the disclosed implementations. Other implementations and applications also are possible, and as such, the following examples should not be taken as definitive or limiting either in scope or setting.

In the following detailed description, references are made to the accompanying drawings, which form a part of the description and in which are shown, by way of illustration, specific implementations. Although these disclosed implementations are described in sufficient detail to enable one skilled in the art to practice the implementations, it is to be understood that these examples are not limiting, such that other implementations may be used and changes may be made to the disclosed implementations without departing from their spirit and scope. For example, the blocks of the methods shown and described herein are not necessarily performed in the order indicated in some other implementations. Additionally, in some other implementations, the disclosed methods may include more or fewer blocks than are described. As another example, some blocks described herein as separate blocks may be combined in some other implementations. Conversely, what may be described herein as a single block may be implemented in multiple blocks in some other implementations. Additionally, the conjunction “or” is intended herein in the inclusive sense where appropriate unless otherwise indicated; that is, the phrase “A, B or C” is intended to include the possibilities of “A,” “B,” “C,” “A and B,” “B and C,” “A and C” and “A, B and C.”

As noted above, hardware configurations for nodes in a server cluster can vary in terms of capabilities, e.g. resources such as disk space, processor power, available memory, etc. Metrics about these resources may be relatively static in nature, such as total disk space, total memory, maximum processor speed, number of processors/processor cores, etc., or may be dynamic in nature, such as current processor loading, number of tasks or threads, remaining disk space, available memory, number of pending I/O requests, etc.

To optimize client latency, transactional messages such as read/write (R/W) requests from clients and associated responses (from server nodes and/or clients) may be distributed across server nodes (or simply, “nodes”) in the server cluster, with requests being dispatched to nodes that are less loaded and/or capable of better performance compared to other nodes. For a client to determine which node or nodes to direct requests, the client may rely upon the foregoing metrics, including dynamic metrics. Effective selection of a node or nodes by a client may be facilitated by up-to-date dynamic metrics of at least a subset of the server cluster nodes.

A client may obtain these up-to-date metrics in a variety of ways. One possible solution is for a client to poll each node or a subset of each node of a cluster directly, on a routine basis, to determine the current state of the dynamic metrics. However, this may in itself pose a significant load on the various nodes in the cluster. Where the cluster consists of tens of thousands of nodes possibly being queried by tens of thousands of clients, the burden of responding to individual load requests from each client to each node could easily consume a sizeable amount of bandwidth that would be better utilized for responding to read/write requests. Moreover, a client initially communicating with the cluster would need to poll at least a suitable number of nodes prior to any read/write request to determine where to submit the request, which may itself impose additional latency. An approach that is possibly less-bandwidth intensive and would resolve the need for a client to do initial polling is for each server to report to a client the metrics (both static and dynamic) associated with all or many nodes in the cluster upon request by the client.

This does not, however, address the problem of regular gathering of metrics from cluster nodes. Where a node reports metrics for multiple nodes, each node could exchange load data with other nodes in the server cluster on a periodic basis. However, this approach may create significant bandwidth usage between nodes (especially as a cluster increases in size), and may, depending upon cluster configuration, require the imposition of additional security measures to secure intra-cluster communications.

As discussed herein, node metrics may be “piggybacked” upon communications from clients, such as transactional messages or R/W requests, allowing for opportunistic dissemination of node metrics. By exchanging all node metrics between a client and a node in piggybacked communications, traffic between a given client and node may be reduced. Where each client may talk to multiple nodes, metric information received from one node may be forwarded to other nodes in future communications. Any out of date information can be updated or refreshed by each node on receipt from a client, and then returned to the providing client following updating to allow the client to update its information. In addition, any supplied metrics will include up-to-date metrics for the providing node. In this way, over time all nodes in a cluster will receive load metrics for the other cluster nodes, and clients may obtain periodically updated load information. Where clients are routinely submitting R/W requests, this data is kept relatively current without requiring inter-node communication or a routine polling by clients, thus potentially conserving bandwidth and improving overall cluster performance.

I. Example System Overview

FIG. 1A shows a block diagram of an example of an environment 10 in which an on-demand database service can be used in accordance with some implementations. The environment 10 includes user systems 12, a network 14, a database system 16 (also referred to herein as a “cloud-based system”), a processor system 17, an application platform 18, a network interface 20, tenant database 22 for storing tenant data 23, system database 24 for storing system data 25, program code 26 for implementing various functions of the system 16, and process space 28 for executing database system processes and tenant-specific processes, such as running applications as part of an application hosting service. In some other implementations, environment 10 may not have all of these components or systems, or may have other components or systems instead of, or in addition to, those listed above.

In some implementations, the environment 10 is an environment in which an on-demand database service exists. An on-demand database service, such as that which can be implemented using the system 16, is a service that is made available to users outside of the enterprise(s) that own, maintain or provide access to the system 16. As described above, such users generally do not need to be concerned with building or maintaining the system 16. Instead, resources provided by the system 16 may be available for such users' use when the users need services provided by the system 16; that is, on the demand of the users. Some on-demand database services can store information from one or more tenants into tables of a common database image to form a multi-tenant database system (MTS). The term “multi-tenant database system” can refer to those systems in which various elements of hardware and software of a database system may be shared by one or more customers or tenants. For example, a given application server may simultaneously process requests for a great number of customers, and a given database table may store rows of data such as feed items for a potentially much greater number of customers. A database image can include one or more database objects. A relational database management system (RDBMS) or the equivalent can execute storage and retrieval of information against the database object(s).

Application platform 18 can be a framework that allows the applications of system 16 to execute, such as the hardware or software infrastructure of the system 16. In some implementations, the application platform 18 enables the creation, management and execution of one or more applications developed by the provider of the on-demand database service, users accessing the on-demand database service via user systems 12, or third party application developers accessing the on-demand database service via user systems 12.

In some implementations, the system 16 implements a web-based customer relationship management (CRM) system. For example, in some such implementations, the system 16 includes application servers configured to implement and execute CRM software applications as well as provide related data, code, forms, renderable web pages and documents and other information to and from user systems 12 and to store to, and retrieve from, a database system related data, objects, and Web page content. In some MTS implementations, data for multiple tenants may be stored in the same physical database object in tenant database 22. In some such implementations, tenant data is arranged in the storage medium(s) of tenant database 22 so that data of one tenant is kept logically separate from that of other tenants so that one tenant does not have access to another tenant's data, unless such data is expressly shared. The system 16 also implements applications other than, or in addition to, a CRM application. For example, the system 16 can provide tenant access to multiple hosted (standard and custom) applications, including a CRM application. User (or third party developer) applications, which may or may not include CRM, may be supported by the application platform 18. The application platform 18 manages the creation and storage of the applications into one or more database objects and the execution of the applications in one or more virtual machines in the process space of the system 16.

According to some implementations, each system 16 is configured to provide web pages, forms, applications, data and media content to user (client) systems 12 to support the access by user systems 12 as tenants of system 16. As such, system 16 provides security mechanisms to keep each tenant's data separate unless the data is shared. If more than one MTS is used, they may be located in close proximity to one another (for example, in a server farm located in a single building or campus), or they may be distributed at locations remote from one another (for example, one or more servers located in city A and one or more servers located in city B). As used herein, each MTS could include one or more logically or physically connected servers distributed locally or across one or more geographic locations. Additionally, the term “server” is meant to refer to a computing device or system, including processing hardware and process space(s), an associated storage medium such as a memory device or database, and, in some instances, a database application (for example, OODBMS or RDBMS) as is well known in the art. It should also be understood that “server system” and “server” are often used interchangeably herein. Similarly, the database objects described herein can be implemented as part of a single database, a distributed database, a collection of distributed databases, a database with redundant online or offline backups or other redundancies, etc., and can include a distributed database or storage network and associated processing intelligence.

The network 14 can be or include any network or combination of networks of systems or devices that communicate with one another. For example, the network 14 can be or include any one or any combination of a LAN (local area network), WAN (wide area network), telephone network, wireless network, cellular network, point-to-point network, star network, token ring network, hub network, or other appropriate configuration. The network 14 can include a TCP/IP (Transfer Control Protocol and Internet Protocol) network, such as the global internetwork of networks often referred to as the “Internet” (with a capital “I”). The Internet will be used in many of the examples herein. However, it should be understood that the networks that the disclosed implementations can use are not so limited, although TCP/IP is a frequently implemented protocol.

The user systems 12 can communicate with system 16 using TCP/IP and, at a higher network level, other common Internet protocols to communicate, such as HTTP, FTP, AFS, WAP, etc. In an example where HTTP is used, each user system 12 can include an HTTP client commonly referred to as a “web browser” or simply a “browser” for sending and receiving HTTP signals to and from an HTTP server of the system 16. Such an HTTP server can be implemented as the sole network interface 20 between the system 16 and the network 14, but other techniques can be used in addition to or instead of these techniques. In some implementations, the network interface 20 between the system 16 and the network 14 includes load sharing functionality, such as round-robin HTTP request distributors to balance loads and distribute incoming HTTP requests evenly over a number of servers. In MTS implementations, each of the servers can have access to the MTS data; however, other alternative configurations may be used instead.

The user systems 12 can be implemented as any computing device(s) or other data processing apparatus or systems usable by users to access the database system 16. For example, any of user systems 12 can be a desktop computer, a work station, a laptop computer, a tablet computer, a handheld computing device, a mobile cellular phone (for example, a “smartphone”), or any other Wi-Fi-enabled device, wireless access protocol (WAP)-enabled device, or other computing device capable of interfacing directly or indirectly to the Internet or other network. The terms “user system” and “computing device” are used interchangeably herein with one another and with the term “computer.” As described above, each user system 12 typically executes an HTTP client, for example, a web browsing (or simply “browsing”) program, such as a web browser based on the WebKit platform, Microsoft's Internet Explorer browser, Apple's Safari, Google's Chrome, Opera's browser, or Mozilla's Firefox browser, or the like, allowing a user (for example, a subscriber of on-demand services provided by the system 16) of the user system 12 to access, process and view information, pages and applications available to it from the system 16 over the network 14.

Each user system 12 also typically includes one or more user input devices, such as a keyboard, a mouse, a trackball, a touch pad, a touch screen, a pen or stylus or the like, for interacting with a graphical user interface (GUI) provided by the browser on a display (for example, a monitor screen, liquid crystal display (LCD), light-emitting diode (LED) display, among other possibilities) of the user system 12 in conjunction with pages, forms, applications and other information provided by the system 16 or other systems or servers. For example, the user interface device can be used to access data and applications hosted by system 16, and to perform searches on stored data, and otherwise allow a user to interact with various GUI pages that may be presented to a user. As discussed above, implementations are suitable for use with the Internet, although other networks can be used instead of or in addition to the Internet, such as an intranet, an extranet, a virtual private network (VPN), a non-TCP/IP based network, any LAN or WAN or the like.

The users of user systems 12 may differ in their respective capacities, and the capacity of a particular user system 12 can be entirely determined by permissions (permission levels) for the current user of such user system. For example, where a salesperson is using a particular user system 12 to interact with the system 16, that user system can have the capacities allotted to the salesperson. However, while an administrator is using that user system 12 to interact with the system 16, that user system can have the capacities allotted to that administrator. Where a hierarchical role model is used, users at one permission level can have access to applications, data, and database information accessible by a lower permission level user, but may not have access to certain applications, database information, and data accessible by a user at a higher permission level. Thus, different users generally will have different capabilities with regard to accessing and modifying application and database information, depending on the users' respective security or permission levels (also referred to as “authorizations”).

According to some implementations, each user system 12 and some or all of its components are operator-configurable using applications, such as a browser, including computer code executed using a central processing unit (CPU) such as an Intel Pentium® processor or the like. Similarly, the system 16 (and additional instances of an MTS, where more than one is present) and all of its components can be operator-configurable using application(s) including computer code to run using the processor system 17, which may be implemented to include a CPU, which may include an Intel Pentium® processor or the like, or multiple CPUs.

The system 16 includes tangible computer-readable media having non-transitory instructions stored thereon/in that are executable by or used to program a server or other computing system (or collection of such servers or computing systems) to perform some of the implementation of processes described herein. For example, computer program code 26 can implement instructions for operating and configuring the system 16 to intercommunicate and to process web pages, applications and other data and media content as described herein. In some implementations, the computer code 26 can be downloadable and stored on a hard disk, but the entire program code, or portions thereof, also can be stored in any other volatile or non-volatile memory medium or device as is well known, such as a ROM or RAM, or provided on any media capable of storing program code, such as any type of rotating media including floppy disks, optical discs, digital versatile disks (DVD), compact disks (CD), microdrives, and magneto-optical disks, and magnetic or optical cards, nanosystems (including molecular memory ICs), or any other type of computer-readable medium or device suitable for storing instructions or data. Additionally, the entire program code, or portions thereof, may be transmitted and downloaded from a software source over a transmission medium, for example, over the Internet, or from another server, as is well known, or transmitted over any other existing network connection as is well known (for example, extranet, VPN, LAN, etc.) using any communication medium and protocols (for example, TCP/IP, HTTP, HTTPS, Ethernet, etc.) as are well known. It will also be appreciated that computer code for the disclosed implementations can be realized in any programming language that can be executed on a server or other computing system such as, for example, C, C++, HTML, any other markup language, Java™, JavaScript, ActiveX, any other scripting language, such as VBScript, and many other programming languages as are well known may be used. (Java™ is a trademark of Sun Microsystems, Inc.).

FIG. 1B shows a block diagram of example implementations of elements of FIG. 1A and example interconnections between these elements according to some implementations. That is, FIG. 1B also illustrates environment 10, but FIG. 1B, various elements of the system 16 and various interconnections between such elements are shown with more specificity according to some more specific implementations. Additionally, in FIG. 1B, the user system 12 includes a processor system 12A, a memory system 12B, an input system 12C, and an output system 12D. The processor system 12A can include any suitable combination of one or more processors. The memory system 12B can include any suitable combination of one or more memory devices. The input system 12C can include any suitable combination of input devices, such as one or more touchscreen interfaces, keyboards, mice, trackballs, scanners, cameras, or interfaces to networks. The output system 12D can include any suitable combination of output devices, such as one or more display devices, printers, or interfaces to networks.

In FIG. 1B, the network interface 20 is implemented as a set of HTTP application servers 1001-100N. Each application server 100, also referred to herein as an “app server”, is configured to communicate with tenant database 22 and the tenant data 23 therein, as well as system database 24 and the system data 25 therein, to serve requests received from the user systems 12. The tenant data 23 can be divided into individual tenant storage spaces 40, which can be physically or logically arranged or divided. Within each tenant storage space 40, user storage 42 and application metadata 44 can similarly be allocated for each user. For example, a copy of a user's most recently used (MRU) items can be stored to user storage 42. Similarly, a copy of MRU items for an entire organization that is a tenant can be stored to tenant storage space 40.

The process space 28 includes system process space 50, individual tenant process spaces 48 and a tenant management process space 46. The application platform 18 includes an application setup mechanism 38 that supports application developers' creation and management of applications. Such applications and others can be saved as metadata into tenant database 22 by save routines 36 for execution by subscribers as one or more tenant process spaces 48 managed by tenant management process 46, for example. Invocations to such applications can be coded using PL/SOQL 34, which provides a programming language style interface extension to API 32. A detailed description of some PL/SOQL language implementations is discussed in commonly assigned U.S. Pat. No. 7,730,478, titled METHOD AND SYSTEM FOR ALLOWING ACCESS TO DEVELOPED APPLICATIONS VIA A MULTI-TENANT ON-DEMAND DATABASE SERVICE, by Craig Weissman, issued on Jun. 1, 2010, and hereby incorporated by reference in its entirety and for all purposes. Invocations to applications can be detected by one or more system processes, which manage retrieving application metadata 44 for the subscriber making the invocation and executing the metadata as an application in a virtual machine.

The system 16 of FIG. 1B also includes a user interface (UI) 30 and an application programming interface (API) 32 to system 16 resident processes to users or developers at user systems 12. In some other implementations, the environment 10 may not have the same elements as those listed above or may have other elements instead of, or in addition to, those listed above.

Each application server 100 can be communicably coupled with tenant database 22 and system database 24, for example, having access to tenant data 23 and system data 25, respectively, via a different network connection. For example, one application server 1001 can be coupled via the network 14 (for example, the Internet), another application server 100N-1 can be coupled via a direct network link, and another application server 100N can be coupled by yet a different network connection. Transfer Control Protocol and Internet Protocol (TCP/IP) are examples of typical protocols that can be used for communicating between application servers 100 and the system 16. However, it will be apparent to one skilled in the art that other transport protocols can be used to optimize the system 16 depending on the network interconnections used.

In some implementations, each application server 100 is configured to handle requests for any user associated with any organization that is a tenant of the system 16. Because it can be desirable to be able to add and remove application servers 100 from the server pool at any time and for various reasons, in some implementations there is no server affinity for a user or organization to a specific application server 100. In some such implementations, an interface system implementing a load balancing function (for example, an F5 Big-IP load balancer) is communicably coupled between the application servers 100 and the user systems 12 to distribute requests to the application servers 100. In one implementation, the load balancer uses a least-connections algorithm to route user requests to the application servers 100. Other examples of load balancing algorithms, such as round robin and observed-response-time, also can be used. For example, in some instances, three consecutive requests from the same user could hit three different application servers 100, and three requests from different users could hit the same application server 100. In this manner, by way of example, system 16 can be a multi-tenant system in which system 16 handles storage of, and access to, different objects, data and applications across disparate users and organizations.

In one example storage use case, one tenant can be a company that employs a sales force where each salesperson uses system 16 to manage aspects of their sales. A user can maintain contact data, leads data, customer follow-up data, performance data, goals and progress data, etc., all applicable to that user's personal sales process (for example, in tenant database 22). In an example of a MTS arrangement, because all of the data and the applications to access, view, modify, report, transmit, calculate, etc., can be maintained and accessed by a user system 12 having little more than network access, the user can manage his or her sales efforts and cycles from any of many different user systems. For example, when a salesperson is visiting a customer and the customer has Internet access in their lobby, the salesperson can obtain critical updates regarding that customer while waiting for the customer to arrive in the lobby.

While each user's data can be stored separately from other users' data regardless of the employers of each user, some data can be organization-wide data shared or accessible by several users or all of the users for a given organization that is a tenant. Thus, there can be some data structures managed by system 16 that are allocated at the tenant level while other data structures can be managed at the user level. Because an MTS can support multiple tenants including possible competitors, the MTS can have security protocols that keep data, applications, and application use separate. Also, because many tenants may opt for access to an MTS rather than maintain their own system, redundancy, up-time, and backup are additional functions that can be implemented in the MTS. In addition to user-specific data and tenant-specific data, the system 16 also can maintain system level data usable by multiple tenants or other data. Such system level data can include industry reports, news, postings, and the like that are sharable among tenants.

In some implementations, the user systems 12 (which also can be client systems) communicate with the application servers 100 to request and update system-level and tenant-level data from the system 16. Such requests and updates can involve sending one or more queries to tenant database 22 or system database 24. The system 16 (for example, an application server 100 in the system 16) can automatically generate one or more SQL statements (for example, one or more SQL queries) designed to access the desired information. System database 24 can generate query plans to access the requested data from the database. The term “query plan” generally refers to one or more operations used to access information in a database system.

Each database can generally be viewed as a collection of objects, such as a set of logical tables, containing data fitted into predefined or customizable categories. A “table” is one representation of a data object, and may be used herein to simplify the conceptual description of objects and custom objects according to some implementations. It should be understood that “table” and “object” may be used interchangeably herein. Each table generally contains one or more data categories logically arranged as columns or fields in a viewable schema. Each row or element of a table can contain an instance of data for each category defined by the fields. For example, a CRM database can include a table that describes a customer with fields for basic contact information such as name, address, phone number, fax number, etc. Another table can describe a purchase order, including fields for information such as customer, product, sale price, date, etc. In some MTS implementations, standard entity tables can be provided for use by all tenants. For CRM database applications, such standard entities can include tables for case, account, contact, lead, and opportunity data objects, each containing pre-defined fields. As used herein, the term “entity” also may be used interchangeably with “object” and “table.”

In some MTS implementations, tenants are allowed to create and store custom objects, or may be allowed to customize standard entities or objects, for example by creating custom fields for standard objects, including custom index fields. Commonly assigned U.S. Pat. No. 7,779,039, titled CUSTOM ENTITIES AND FIELDS IN A MULTI-TENANT DATABASE SYSTEM, by Weissman et al., issued on Aug. 17, 2010, and hereby incorporated by reference in its entirety and for all purposes, teaches systems and methods for creating custom objects as well as customizing standard objects in a multi-tenant database system. In some implementations, for example, all custom entity data rows are stored in a single multi-tenant physical table, which may contain multiple logical tables per organization. It is transparent to customers that their multiple “tables” are in fact stored in one large table or that their data may be stored in the same table as the data of other customers.

FIG. 2 shows a simplified block diagram of a cluster 220 of servers (Nodes 1-M) in a distributed data storage system. In some embodiments, a data storage system may correspond to data storage elements 22, 24 described above. For illustration, an internal network 200 is provisioned to support communications, including but not limited to messaging and data transfer, among clients 210, numbered C1-C100. These numbers of clients and servers are not critical or limiting; they are merely illustrative. In this figure, the clients are “internal” to a system, such as system 16 in FIG. 1A; they are not clients associated with external user systems 12.

A client in general may be defined as a piece of computer hardware and/or software that accesses a service made available by a server. Clients 210 may be coupled to an internal network 200, i.e., a system network that is not exposed to external clients. A server is often (but not always) on another computer system, in which case the client may access the service by way of a network. In FIG. 2, networking between the clients and the cluster nodes is omitted for simplicity. Nonetheless, each of the clients 210 has access to the data storage cluster 220. More specifically, each client is able to communicate (for example, exchange messages, data packets, etc.) In practice, there may be thousands of nodes in a single cluster, and there may be many clusters in a system. In some embodiments, a cluster may be partitioned in “racs” (Rac 1, Rac 2, etc.) RAC stands for Real Application Clusters, a version of Oracle database. In some embodiments, a cluster may include replica nodes, where stored data is duplicated, for high reliability or availability. The number of nodes (and clusters) is likely to vary dynamically, as resources are added (brought online) or conversely, resources may be retired or fail.

In a typical heterogeneous system, the individual nodes, which may be servers, have various capabilities. Hardware configurations can vary on storage capacity, storage efficiency, performance, network bandwidth, network performance, number of CPU cores, CPU capabilities, clock rate, amount of memory. Even where servers have similar static capabilities, their current status or loading may vary considerably. For example, when new servers are added to the cluster, they may have large storage capacity available, as they have not yet received write messages. Other existing servers may be nearly full, so immediately there is an imbalance in the cluster. However, simply sending all new writes to the new server(s) may be imprudent, as they be limited by CPU loading, network traffic or other factors. Thus, dynamic variations can be based on current CPU load on the machine, amount of free memory on the system, percentage of network saturation, etc. So it is extremely inefficient to consider all these machines in the same way while distributing work across this cluster.

Regarding FIG. 3A, as described in more detail below, it illustrates some examples of static server node metrics that may be used in realizing some embodiments consistent with the present disclosure. One aspect of the present disclosure calls for collecting metrics about the server nodes in a given cluster. Metrics may collected by each of the clients. Metrics data may be stored in local memory, DRAM, flash, or any other memory means accessible to the client. In some embodiments, this data may comprise a static configuration record 302 for each server node. The record 302 may include the following fields, for example, the server node network bandwidth 310, storage capacity 312, number of CPU cores 314, clock rate 320, and other metrics. These are static characteristics of a hardware configuration; they generally do not change in the context of the present disclosure.

Referring now to FIG. 3B, it illustrates some examples of dynamic server node metrics that may be used in realizing some embodiments consistent with the present disclosure. A table 330 may have a record 332 for some, or preferably all, of the nodes in the cluster. Each record 332 may have an identifier field “UID” for the corresponding node. The record may include (or link or associate to) the static hardware configuration of the node. The hardware configuration may be similar to the illustration in FIG. 3A. In addition, the record may include (or link or associate to) dynamic metrics for the corresponding node, field 336. This field may include, for example, various dynamic metrics such as CPU load, percentage network saturation, and free memory. Other metrics may be used as well. A timestamp 340 indicates the time at which the dynamic metrics were collected. The timestamp may be provided by the reporting server node, or added by the client, although the former may be more accurate.

FIG. 4A is a simplified conceptual diagram illustrating a client entity 210 collecting metrics data 406 from each of the server nodes in a cluster 220. In an embodiment, a query message essentially asks the server node to which it is directed to reply to the inquiring client with current (dynamic) metrics about the server. These metrics may include some of those mentioned above. The specific details and protocols for these exchanges may vary with different applications and are a matter of design choice. Dynamic node metric data collection by the clients can be implemented in various ways. Some examples are described below, including a scheduled or periodic approach, an event driven approach, an opportunistic approach, was well as any combination of these features. In some embodiments, each of the clients may collect metrics from each of the server nodes. In other embodiments, node metrics may be delivered in other ways, for example, via a centralized system, pushed externally via a 3^(rd) service, gossip-style, etc. However the node metrics data is provided, these features enable each client to make autonomous decisions for allocating loading or access requests (for example, memory write requests) among the server nodes. In this way, the allocation decisions are distributed rather than centralized and each client is “aware” of current conditions at various nodes in the cluster.

FIG. 4B illustrates a data table 450 storing server metrics. The structure and arrangement of the table are not critical. Indeed, some embodiments may not utilize a table structure to store this data at all. In this example, table 450 includes a record or row for each server node, identified at 452 as SERVER NODE 1-SERVER NODE M. Each record may include a metrics timestamp 458, and one or more dynamic node metrics, illustrated as Metric 1 (460) . . . Metric N (462). The metrics may include those described with regard to FIG. 3B. During operation, the timestamp and metrics for a given server node will be updated repeatedly to reflect the most current data reported.

FIG. 5A is a simplified flow diagram of an example client process for resource aware load distribution in a distributed system of the type described. At block 502, a client sends a periodic metrics query message to each server node in the cluster. The loop 503 is to illustrate that the process 502 may be repeated periodically. The frequency (period) preferably is tunable. Higher frequency of periodic metrics queries will provide more accurate (up to date) information about each node's metrics. However, one of the drawbacks of retrieving these metrics on a very high frequency, for example, every minute or every 5 minutes, is that in larger clusters with 1000s of storage servers and clients, there may be millions of such query packets every few minutes. In some embodiments, this volume may impact system performance. Below we describe some processes to mitigate the volume of queries. The client receives replies from the server nodes containing the corresponding node metrics, block 504.

Based on the acquired node metrics (which may be stored as discussed above), the client assigns a value or weight to each node, block 506. For example, nodes with higher free disk space and lower IO utilization are given higher weights than those with lower free disk space or the ones with high free disk space but high 10 utilization. In another example, nodes with better network bandwidth capabilities may be assigned more write requests than similarly capable nodes with lower network bandwidth. Similar decisions can be taken while directing a read request to one of the replica nodes. These processes lead to more balanced placement of data within the cluster and also leads to more effective usage of the resources.

In general, various metrics may be used, or combined with others, to generate the weights to be assigned. Preferably, the weights are generated programmatically for speed, using predetermined algorithms. For example, linear equations may be used to combine various metrics, utilizing various coefficients or parameters to control the influence of each metric. These parameters may be tunable; and they may be developed or “learned” experimentally.

Piggyback

There are several ways of collecting the metrics in addition to (or combined with) explicitly querying each of the servers periodically (“periodic metrics query”) as described above. One alternative we call “piggybacking,” as follows. In some embodiments, the storage servers send their metrics to clients piggy-backed on (appended to) responses to regular read/write requests. This reduces the number of explicit requests to be sent; those explicit requests (the periodic metrics query) may be sent to only those servers with which the client isn't actively communicating, or had not communicated recently. FIG. 5B is a simplified flow diagram of an example server node process to piggyback local metrics in a response to a R/W request. A server receives a R/W request from a client, block 540. The server node assembles current local node metrics, block 542. Generally these would by dynamic metrics as discussed above. The server node prepares a response to the R/W request, in the usual known fashion (a “regular response”), block 544. Further, the server appends or “piggybacks” the local metrics on to the regular response, block 548. Then the response, including the node metrics, is returned to the requesting client, block 550. In this way, periodic metric queries need not be sent, or they may be deferred, to nodes where R/W requests and replies recently occurred. In some cases, a node may be programmed to piggyback metrics on every reply it sends. In other embodiments, a node may append piggyback metrics only when requested to do so in the R/W request message. FIG. 6A is a simplified conceptual diagram illustrating request and reply messaging between a client and a server node. Here, a client 210 (C2) sends a request message 606, and the server (Node 3 for illustration) sends a reply 610 with metrics as described. FIG. 6B is a simplified conceptual diagram illustrating a read reply packet 610 with appended (piggyback) server node metrics.

In some embodiments, the client “expires” metrics that have a timestamp that is deemed too old. For example, the timestamp may reflect an age that exceeds a default or nominal frequency of the periodic metrics query. The expiration may trigger an asynchronous explicit metrics query. FIG. 7 is a simplified flow diagram of an example client process for maintaining current server node metrics to improve resource aware load distribution in a distributed system. Here, a client may receive node metrics from a server node, block 702. The client may update a server metrics table with the new metrics data and updated timestamp, block 704. In some embodiments, the table may be similar to the illustration of FIG. 4B.

The client may check the metrics table for expired timestamps, for example, those older than a predetermined age, block 706. If none are found, the process may loop via path 712. If an expired timestamp is found, decision 710, the client process identifies the corresponding server node (for example, using the identifier in the table), block 714. Then, the client may send an explicit metric query message to the identified node, block 720, in order to update the server metrics. In another (asynchronous) embodiment, an expired timestamp may trigger an event message to the client, event 724. The client may then execute the steps 714 and 720 as discussed.

Allocating Requests to Server Nodes

FIG. 5C is a simplified flow diagram of an example process for a client to allocate a request to a server node in a distributed data storage system, in accordance with some embodiments. Here, a client generates a write request, block 560. The client accesses its own ranked list of server nodes, block 562. The list may be ranked according to the weights described above. Recall, the weights, and thus the ranking, is updated dynamically based on server metrics. The client selects a highest ranked server node, block 566. Next the client may apply one or more allocation policies to the pending write request, block 570.

In some embodiments, the weights may be divided into groups. For example, a highest weight group may be assigned probabilities, for example, 0.9 to 1.0. A second group may be assigned probabilities 0.8 to 0.9, and so on. Then, a write request may be allocated to the highest level group. Within that group presumably there are many server nodes. An individual server node within the group may be selected by various means, for example, randomly.

In some embodiments, depending on the type of use case, the allocation policies may include one or more of the following:

-   -   A. Free disk space aware: If the cluster takes mostly write only         traffic, we can distribute the load such that the nodes with         higher free disk space get more writes than the ones with lower         free disk space.     -   B. CPU load based distribution: If the load being distributed         within the cluster is CPU bound, the distribution should take         into account such metrics as the average CPU utilization over         the last 60 seconds and distribute load more to nodes with lower         average CPU utilization.     -   C. Network bandwidth based distribution: If the nodes in the         cluster are more or less identical in most respects but have         different network bandwidth capabilities or they are located in         data centers with different ingress/egress network bandwidth, in         such cases the distribution could be based on network bandwidth         as a weight.     -   D. Combination: If the workload is mixed with a comparable mix         of read and write traffic, the weights could be derived using a         combination of some of the above: free disk space, avg. 10         utilization, avg. CPU utilization, etc.     -   E. Rack-aware. If the allocation policy is rack-aware, it should         be taken into account while selecting a server for placement of         load. For example, two nodes from the same rack may have the two         largest weights in the cluster. Preferably, the policy would         ensure selection of nodes from different racks even where the         second node selected doesn't have the second highest weight.

These and other policies may be realized by applying them to determine or adjust the individual node weights, based in part on some or all of the other node metrics, as illustrated above. Another policy relates to sending requests to a new server, i.e., one that recently came on-line in a cluster. A new server would have a large amount of free storage space, which would tend to increase its weight. However, if many clients send requests to the same new server, it may quickly become overloaded, for example, in terms of bandwidth. Decision 572 checks for this situation. For example, the client may count a number of write requests sent to a new server, at least for an initial period of time. If the server is being overloaded, the process may loop back via 573 to select a different server. If the selected server is not overloaded, the process continues to allocate the request to the selected server node, block 574. A counter may be updated when the request is allocated to an identified new server, block 578, to prevent overloading. Finally, the process concludes at 580.

Hot Potato

Despite the distributed set of clients trying their best to place the data as well as they could, we could end up with some nodes becoming overloaded. In such cases, the overloaded server/node receiving such requests can explicitly reject such requests with an error message saying it is overloaded. The clients can then resend such requests to other relatively lightly loaded nodes/servers. The client can then update the metrics for the overloaded server such that its weight reduces. This feature makes the clusters very dynamic and would start responding to changes very quickly by shifting the load from overloaded systems to nodes with lighter loads.

Gossip-Type Dissemination

As described above, server node metrics, as part of client stored or server stored metric information, may be piggybacked upon transactional requests between a client and a server node. This enables implementation of an opportunistic gossip-type mechanism for disseminating server node metrics across all cluster nodes without requiring direct node to node/inter-node communication, or discrete requests from clients for server node metrics. It is considered opportunistic as it relies upon client-node communications unrelated to dissemination of server node metrics, rather than communications specifically for dissemination of metrics. The use of a gossip-type dissemination of server node metrics may reduce overhead of network traffic by reducing the number of required non-transactional messages, viz. messages that are unrelated to a client-server transaction, that are only for disseminating node metrics.

FIG. 8 depicts one embodiment of a system implementing a gossip-type mechanism for disseminating server node metrics, where dissemination is handled by piggybacking metrics upon routine transactional requests and replies, such as read/write (R/W) requests and replies, between a client and a server node. Specifically, FIG. 8 depicts the fundamental interaction between a client 210 and a node 202. A person skilled in the relevant art will understand that the basic steps depicted in FIG. 8 may be repeated across multiple nodes 202, and, as will be described in more detail herein, such repetition will result in ongoing dissemination and updating of server metric information across a cluster of server nodes, cluster 220.

The system may include a cluster 220 of server nodes 202 (denoted as NODE1 to NODE4, by way of example), each capable of communicating with a plurality of clients 210 (denoted as clients C1 to C100, by way of example). Each server node 202 of the cluster 220 of server nodes may include server metrics on at least itself, and possibly other nodes 202 of cluster 220. Each server node 202 and client 210 may be implemented as a user system or server, such as those described above with reference to FIGS. 1A and 1B. As depicted in FIG. 8, clients C1 to C100 may optionally be connected together via an internal network 200 in one embodiment. Such embodiments may be deployed where cluster 220 and internal network 200 are commonly owned by a single entity or by closely related entities.

Other embodiments may have clients 210 each be essentially stand-alone, with network connectivity between various clients C1 to C100 only incidentally provided insofar as each client may be connected to the Internet. In such embodiments, each client 210 may contact cluster 220 via the Internet, for example, where cluster 220 is available as part of a cloud platform or software as a service (SaaS) offering, and clients 210 may be owned by a variety of different subscribers to the cloud platform or SaaS offering. Other possible configurations may be realized without departing from the scope of this disclosure.

Each node 202 may be configured to receive a metrics query message 802, which may be initiated by one of the clients 210. In the depicted embodiment, the metrics query message 802 may be piggybacked onto a transaction request message, such as a read or write (R/W) request, from one of the plurality of clients, issued by a client 210 as part of utilizing services offered by cluster 220. Other embodiments may allow metrics query message 802 to be issued as a standalone message. Still other embodiments may employ a combination of standalone and piggybacked messages, utilized as client and/or cluster needs arise. The metrics query message, as will be described in greater detail below, may include any client stored metric information, which may include metrics from one or more server nodes other than node 202 that is currently contacted. This may be the case where client 210 has been in communication with cluster 220 long enough to have communicated with one or more nodes 202. Where node 202 is the first node contacted by client 210, such as where client 210 is first accessing cluster 220, client 210 may not have any stored metric information, and so may simply send a request to a node 202 to transmit its stored metric information.

Following receipt of a metrics query message 802 and (potentially) associated client stored metric information, node 202 may be configured to reconcile its server stored metric information with the received client stored metric information (if any), and transmit a reply 804 to client 210 that includes updated metric information. In some embodiments, the updated metric information may include a list of metrics that have been updated or are missing from the client stored server metrics. In other embodiments, the updated metric information may also include a list of one or more server metrics to delete from the client stored metric information, where, for example, a server node may have been taken off-line or otherwise removed from the cluster. In still other embodiments, the updated metric information may be the entire server stored metric information following reconciliation.

As with the metrics query message 802, the updated metric information may be piggybacked as a metrics update message onto reply message 804 (such as a R/W reply), to the client 210. The metrics update message may include at least the current metrics for the responding first server node, node 202 (shown as “NODE3”). The metrics update message may also include any server metric information that node 202 may possess for other nodes 202. Node 202 may have obtained the metric information on other nodes by, for example, prior contact with client 210 or another client 210, such as a CLIENT C1.

Upon receipt of the metrics update message via reply message 804, the receiving client 210 may update its client stored metric information with the updated metric information received in the metrics update message. Where the metrics update message includes metrics for server nodes 202 that are not currently in the client stored metric information, those missing metrics may be added to the client stored metric information. If client 210 did not have any metrics to supply with the initial metrics query message, then, in some embodiments, the metrics update message may include all server metrics stored by node 202, in addition to node 202's local metrics. First server node 202 would supply the entirety of its server stored metric information, which client 210 would simply accept and designate as its client stored metric information. It will be appreciated that, in embodiments, the metrics update message may have at least one server node metric, that of responding first server node 202 that generated the metrics update message.

Although FIG. 8 depicts client 210 initiating the exchange of metric information and performing the comparison, it should be understood that the roles could be substantially reversed, viz. the node 202 could transmit its server stored metric information upon initial contact rather than in response to a metrics query message 802, with client 210 performing the comparison of metrics received from the node with its client stored metric information, then transmitting update metric information to node 202.

It should further be understood that in generating a metrics update message 804, node 202 (or client 210, if the roles are reversed) may update its own stored metric information, and likewise the client 210 that receives the metrics update message 804 may update its client stored metric information. The result following the exchange, then, would have both client 210 and node 202 with substantially identical stored server metrics, including at least the most current metrics for node 202.

These interactions may be repeated subsequently for other nodes 202 that client 210 may contact. In FIG. 8, NODE4, a second server node, may be contacted by client 210 following interaction with NODE3. NODE4 node 202 would receive a metrics query message 806 including the client stored metric information that may be comparable in nature to metrics query message 802, and NODE4 may respond with a second metrics update message 808, comparable in nature to first metrics update message 804. All the foregoing steps of interaction between client 210 and NODE3 would be repeated for NODE4. Further, over time client 210 may contact any number of nodes 202 in server cluster 220, and the communications exchange may be substantially identical for each node 202 as it is with NODE3.

FIG. 9 depicts the flow for a method 900 of disseminating server node metrics using gossip-style communication. Some or all of the operations of method 900 may be carried out with various components of the system of FIG. 8, including a client 210 and a plurality of server nodes 202.

In block 902, a client 210 may send a recipient, such as a first server node (herein, node 202) a metrics query message, as described above with reference to FIG. 8. This message may be piggybacked upon a transactional request message, such as client 210 may issue to commence or further a transaction with node 202, the transaction possibly being related to services being offered via server cluster 220. FIG. 6B depicts an embodiment of a structure of a message 610 with piggybacked client stored metric information and/or a metrics query message. Message 610 is one possible embodiment of how a metrics query message and/or client stored metric information may be piggybacked upon a R/W or transactional request message. It will be understood that fields such as “READ REPLY HEADER” and “READ DATA” in message 610 may vary depending upon the specific nature of message 610, e.g. the header and data may correspond instead to a write request with write data, or a request to initiate a transaction that may involve reads and/or writes, or another message related to the services offered by server cluster 220. The metrics query message may include client stored metric information, if client 210 is storing any such metrics. In block 904, the node 202 may receive the metrics query message sent from client 210 in block 902, following extraction of the metrics query message from the transactional message/R/W query.

In block 906, node 202 may obtain its current metric information, as described above: processor loading, available storage, pending I/O requests, etc. Node 202 may also retrieve any server stored metric information in its possession that relate to other nodes 202 in cluster 220. Node 202 may have received metric information from prior transactions with client 210, or another client in communication with cluster 220. The server stored metric information may comprise one or more server metrics that relate to and are associated with any number of different nodes 202. One possible structure of such server stored metric information is depicted in FIG. 4B, as data table 450 showing server metrics. As seen in FIG. 4B, each stored metric may have an identifier of the server node to which the metric relates, and a varying timestamp. It will be appreciated by a person skilled in the relevant art that the various metrics may not reflect the current loading of their particular associated node 202. The older the timestamp is with respect to a current time for a given stored metric, the less likely the stored metric accurately reflects the current loading of its associated node 202.

Node 202 may compare each metric in the received client stored metric information (if any) with server metrics it may have in its server stored metric information. From this comparison, the node 202 may, in various embodiments, generate an updated metric information for transmission in a metrics update message. As will be described in greater detail herein with respect to FIG. 10, the metrics update message may be generated by comparing the timestamps associated with each server metric in the client stored metric information received from the message 802 with the timestamps associated with each corresponding server metric in the server stored metric information by the node 202, and replacing server metrics stored by the node 202 with newer metrics from the client stored metric information received with the metrics query message. While generating the updated metric information, node 202 may also update its stored server metrics.

In block 908, node 202 prepares the metrics update message for transmission to client 210, including adding or updating its current metrics, with the resulting metrics update message comprising updated metric information that includes one or more changed or new server metrics. In other embodiments, node 202 may, following updating, simply copy the entirety of its server stored metric information as the updated metric information for the metrics update message. Node 202 then may add its current metrics to the updated metric information, if it hasn't already, into the metrics update message for transmission to client 210.

As with the client stored metric information transmitted with a metrics query message, the metrics update message may be piggybacked to a transactional reply message (such as an R/W reply) for client 210 in block 910, thus helping conserve bandwidth. The piggybacking structure may be implemented as the previously discussed message 610, depicted in FIG. 6B. The reply message may relate to an ongoing transaction between client 210 and node 202, and may in some embodiments be a response or reply relating to an R/W request message used to transmit the initial metrics query message. In other embodiments, the reply message may relate to a transaction unrelated to the initial request message of block 902. Finally, the reply message with the updated metric information may be sent to client 210 in block 912.

In some instances, the comparison of block 906 may indicate that all server metric information is up to date when compared to the client stored server metrics received from client 210. In such an event, blocks 908 and 910 may be skipped or omitted, with either a simple acknowledgement message of no updates being supplied in some embodiments, or no message being sent in other embodiments.

In block 914, the client 210 may update its client stored metric information with metrics from the updated metric information received in the metrics update message. In some embodiments, the updated metric information includes only those server metrics that are newer (as determined by each metric's timestamp), so all that client 210 would need to do is substitute any metrics in its client stored metric information with the corresponding metrics from the updated metric information. In other embodiments where node 202 simply transmitted the entirety of its server stored metric information as the updated metric information, client 210 may either go through each of the server metrics in the updated metric information received from node 202 and determine which of the server metrics in its client stored metric information need to be updated with newer metrics, from node 202, as per the process of FIG. 10, or alternatively, can simply replace its client stored metric information with the updated metric information.

Finally, following completion of block 914, method 900 may iterate 916 back to block 902. The blocks of method 900 may be repeated by a client 210 with a second or other server node 202. As will be appreciated from the following description, with each discrete server node 202 that client 210 engages via method 900, the server metric information is further updated and disseminated. Following completion of an iteration of method 900, both node 202 and client 210 may store substantially identical server metric information.

It should be understood that some steps of method 900 may be omitted in some embodiments, and/or depending on whether either node 202, client 210, or both contain stored server metric information. For example, if a client 210 is the first client to contact a node 202, node 202 does not currently contain any server stored metric information, and client 210 itself has no client stored metric information, blocks 904-912 may only result in node 202 sending its own server metrics as the updated metric information, with no metric information relating to other server nodes. In lieu of client 210 updating stored metric information (that it doesn't have) in block 914, client 210 may simply save the received metric information from node 202 as its client stored metric information. It will also be appreciated that, in embodiments where the updated metric information comprises the entirety of node's 202 server stored metric information, client 210 may simply save the received metric information from node 202 for each instance of block 914, as mentioned above.

In a subsequent contact by client 210 to a second node 202 of cluster 220, if second node 202 does not have any server stored metric information, it may simply store the client stored metric information transmitted as part of the metrics query message, and again respond with just its current node metrics in block 912. Client 210, which only has client stored metric information for first node 202, may again simply add the current metrics of second node 202 to its client stored metric information. Alternatively, second node 202 may accept the client stored metric information as its server stored metric information, add its current metrics, and then transmit second update metric information in the metrics reply message to client 210.

Following completion of method 900 with a second node 202, in the described example, client 210 will have at least server stored metric information for first node and second node 202, and second node 202 will have at least server stored metric information for the first node (in addition to its own metrics). It will be appreciated that first node 202 will not have metric information on second node 202 until it is contacted by a client 210 with client stored metric information that includes server metrics for second node 202, as discussed below.

If client 210 then re-connected with first node 202, client 210 could supply the metric information for the second node to first node 202 as part of a metrics query message in block 902, receive updated metric information for the first node 202 in block 912, and update its own server stored metric information for the first node in block 914. Moreover, if first node 202 had been in contact with other clients prior to client 210 reconnecting with first node 202, client 210 could potentially receive metric information from first node 202 that were obtained by first node 202 from the other clients in contact with first node 202.

A person skilled in the relevant art will recognize that where method 900 is repeated on an ongoing basis by multiple clients in contact with each of the various nodes 202 of cluster 220 (denoted by iteration line 916), after sufficient time and repeat interactions between clients 210 and nodes 202, each node 202 will contain a set of server stored metric information for all, or nearly all, nodes 202 that are part of server cluster 220. Further ongoing repeats of method 900 will ensure that the server stored metric information of each node are periodically refreshed with more current load metrics from other nodes.

As the approach described herein is opportunistic, it will further be understood that server metric information may be disseminated more rapidly and updated more rapidly where cluster 220 is subject to high loading resulting from a high volume of transactions between clients and nodes of cluster 220. Clients 210 may select various different nodes in cluster 220 to contact for transactions based on weighting of metrics, as described earlier above. Where a cluster 220 is relatively unloaded with few transactions, server metric information may disseminate slowly, if at all. This, however, may not pose a problem; if cluster 220 is relatively unloaded, as will be appreciated, the various nodes of cluster 220 may each be able to handle incoming transaction requests with sufficient expedience that distributing transactions across the nodes of cluster 220 does not result in unacceptable latency.

Referring to FIG. 10, a possible method 1000 of reconciling client stored metric information with server stored metric information that may be performed by a node 202 (or client 210, in some embodiments), in whole or in part, is disclosed. Each stored metric information, comprised of a set of one or more server metrics, stored by either client 210 or a node 202 may contain multiple entries, each entry corresponding to a particular node 202 in cluster 220. This layout is visually depicted in FIG. 4B. Starting in block 1002, for a first entry in the client stored metric information received from a client 210, the node 202 compares the timestamp 458 with the timestamp 458 of a corresponding entry stored by node 202 in its server stored server metrics. Correlation may be made via node identity field 452, which identifies the particular node to which the metrics relate. If no corresponding entry is found by node 202 in its server stored metric information (e.g. this is the first time the metrics for the particular node have been disseminated to node 202), then node 202 may simply copy the metric received from client 210 to its server stored metric information, and proceed to block 1008.

In block 1004, the node 202 may select the metric with the most recent timestamp 458 from between the corresponding entries in the client stored metric information received from client 210 and the server stored metric information of node 202. If the server metric received from client 210 is newer than the corresponding metric currently stored by node 202, node 202 may update its server stored metric information with the entry from client 210, per block 1006. In embodiments where the updated metric information to be sent by node 202 comprises a list of differences, if the server metric received from client 210 is older than the metric currently stored by node 202, node 202 may flag its stored metric for subsequent sending to client 210 as part of the updated metric information. Likewise, if the server stored metric information contains server metrics for nodes 202 that are not present in the received client stored metric information, node 202 may flag such missing metrics for inclusion in the updated metric information.

In block 1008, node 202 determines whether metrics relating to other/additional servers are part of the client stored metric information received from client 210 and if so, may iterate back to block 1002 for each remaining metric from the client stored metric information received from client 210.

If there are no further remaining metrics from the server metrics received from client 210, node 202 may proceed to block 1010, where it prepare the metrics update message. As discussed above, in some embodiments, the metrics update message may simply comprise a copy of the node's 202 server stored metric information. In other embodiments, each selected metric from block 1004 that was found in node 202's stored metrics is added to the updated metric information, as well as any other metrics that may have been in node 202's stored metrics but not in the client stored server metrics received from client 210.

Following completion of all iterations of method 1000 for a given set of received client stored metric information, node 202 will have up-to-date server stored metric information with respect to client 210. In some embodiments the resulting updated metric information will have all entries that are newer than those in the client stored metric information received from client 210, as well as any additional entries that may not have been present in the client stored metric information from client 210. As described above, in other embodiments block 1010 may be effectively skipped, where instead the updated server stored metric information of node 202 may be simply be copied in its entirety as the updated metric information, with client 210 responsible for reconciling its client stored metric information with newer data from the updated metric information.

As suggested above, the various steps of methods 900 and 1000 may be performed by either node 202 or a client 210, and the foregoing description of some possible embodiments is not otherwise intended to limit where particular steps of methods 900 and 1000 are performed.

The specific details of the specific aspects of implementations disclosed herein may be combined in any suitable manner without departing from the spirit and scope of the disclosed implementations. However, other implementations may be directed to specific implementations relating to each individual aspect, or specific combinations of these individual aspects. Additionally, while the disclosed examples are often described herein with reference to an implementation in which an on-demand database service environment is implemented in a system having an application server providing a front end for an on-demand database service capable of supporting multiple tenants, the present implementations are not limited to multi-tenant databases or deployment on application servers. Implementations may be practiced using other database architectures, i.e., ORACLE®, DB2® by IBM and the like without departing from the scope of the implementations claimed.

It should also be understood that some of the disclosed implementations can be embodied in the form of various types of hardware, software, firmware, or combinations thereof, including in the form of control logic, and using such hardware or software in a modular or integrated manner. Other ways or methods are possible using hardware and a combination of hardware and software. Additionally, any of the software components or functions described in this application can be implemented as software code to be executed by one or more processors using any suitable computer language such as, for example, Java, C++ or Perl using, for example, existing or object-oriented techniques. The software code can be stored as a computer- or processor-executable instructions or commands on a physical non-transitory computer-readable medium. Examples of suitable media include random access memory (RAM), read only memory (ROM), magnetic media such as a hard-drive or a floppy disk, or an optical medium such as a compact disk (CD) or DVD (digital versatile disk), flash memory, and the like, or any combination of such storage or transmission devices. Computer-readable media encoded with the software/program code may be packaged with a compatible device or provided separately from other devices (for example, via Internet download). Any such computer-readable medium may reside on or within a single computing device or an entire computer system, and may be among other computer-readable media within a system or network. A computer system, or other computing device, may include a monitor, printer, or other suitable display for providing any of the results mentioned herein to a user.

While some implementations have been described herein, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present application should not be limited by any of the implementations described herein, but should be defined only in accordance with the following and later-submitted claims and their equivalents. 

What is claimed is:
 1. A server node comprising: a processor; and memory coupled to the processor and storing instructions that, when executed by the processor, are configurable to cause the server node to perform operations comprising: receiving client-stored metric information from a client of a plurality of clients, the client-stored metric information being piggybacked onto a read or write (R/W) request from the client; reconciling the client-stored metric information with metric information that is stored by the server node; generating updated metric information; and transmitting the updated metric information to the client piggybacked onto a R/W reply from the server node.
 2. The server node of claim 1, wherein the client-stored metric information is previously updated based on metric information from a second server node.
 3. The server node of claim 1, wherein the client-stored metric information and the metric information stored by the server node each comprise a plurality of server metrics, wherein at least two of the plurality of server metrics in the client-stored metric information relate to different server nodes, and wherein at least two of the plurality of server metrics in the metric information stored by the server node relate to different server nodes.
 4. The server node of claim 3, wherein reconciling the client-stored metric information with the metric information stored by the server node includes comparing each of the plurality of server metrics in the client-stored metric information with each of the plurality of server metrics in the metric information stored by the server node.
 5. The server node of claim 3, wherein each of the plurality of server metrics in the client-stored metric information and each of the plurality of server metrics in the metric information stored by the server node has a timestamp and node identity field.
 6. The server node of claim 5, wherein reconciling the client-stored metric information with the metric information stored by the server node includes comparing at least one server metric in the client-stored metric information with at least one server metric in the metric information stored by the server node that have identical node identity fields.
 7. The server node of claim 6, wherein reconciling the client-stored metric information with the metric information stored by the server node further comprises selecting for transmission, from the server metrics in the client-stored metric information and metric information stored by the server node that have identical node identity fields, a server metric that has a most recent timestamp.
 8. The server node of claim 1, wherein the updated metric information includes the metric information stored by the server node following reconciliation with the client-stored metric information.
 9. The server node of claim 1, wherein the updated metric information comprises a list of changes between the client-stored metric information and the metric information stored by the server node.
 10. A tangible, non-transitory computer-readable medium storing instructions that, when executed by a server node, are configured to cause the server node to perform operations comprising: receiving client-stored metric information from a client of a plurality of clients, the client-stored metric information being piggybacked onto a read or write (R/W) request from the client; reconciling the client-stored metric information with metric information that is stored by the server node; generating updated metric information; and transmitting the updated metric information to the client piggybacked onto a R/W reply from the server node.
 11. The tangible, non-transitory computer-readable medium of claim 10, wherein the client-stored metric information is previously updated based on metric information from a second server node.
 12. The tangible, non-transitory computer-readable medium of claim 10, wherein the client-stored metric information and the metric information stored by the server node each comprise a plurality of server metrics, wherein at least two of the plurality of server metrics in the client-stored metric information relate to different server nodes, and wherein at least two of the plurality of server metrics in the metric information stored by the server node relate to different server nodes.
 13. The tangible, non-transitory computer-readable medium of claim 12, wherein reconciling the client-stored metric information with the metric information stored by the server node includes comparing each of the plurality of server metrics in the client-stored metric information with each of the plurality of server metrics in the metric information stored by the server node.
 14. The tangible, non-transitory computer-readable medium of claim 12, wherein each of the plurality of server metrics in the client-stored metric information and each of the plurality of server metrics in the metric information stored by the server node has a timestamp and node identity field.
 15. The tangible, non-transitory computer-readable medium of claim 14, wherein reconciling the client-stored metric information with the metric information stored by the server node includes comparing at least one server metric in the client-stored metric information with at least one server metric in the metric information stored by the server node that have identical node identity fields.
 16. The tangible, non-transitory computer-readable medium of claim 15, wherein reconciling the client-stored metric information with the metric information stored by the server node further comprises selecting for transmission, from the server metrics in the client-stored metric information and metric information stored by the server node that have identical node identity fields, a server metric that has a most recent timestamp.
 17. The tangible, non-transitory computer-readable medium of claim 10, wherein the updated metric information includes the metric information stored by the server node following reconciliation with the client-stored metric information.
 18. The tangible, non-transitory computer-readable medium of claim 10, wherein the updated metric information comprises a list of changes between the client-stored metric information and the metric information stored by the server node.
 19. A method comprising: receiving, by a server node, client-stored metric information from a client of a plurality of clients, the client-stored metric information being piggybacked onto a read or write (R/W) request from the client; reconciling, by the server node, the client-stored metric information with metric information that is stored by the server node; generating, by the server node, updated metric information; and transmitting, by the server node, the updated metric information to the client piggybacked onto a R/W reply from the server node.
 20. The method of claim 19, wherein the client-stored metric information and the metric information stored by the server node each comprise a plurality of server metrics, wherein at least two of the plurality of server metrics in the client-stored metric information relate to different server nodes, and wherein at least two of the plurality of server metrics in the metric information stored by the server node relate to different server nodes. 